Thank you very much for the feedback! My idea with this game was to make a simple game with 6 stages and the mechanics in place, then go for something more complex which can evolve a bit from the formula... but I'd love to add something more unique for this one too, which also sets a precedent for the next.
The specific challenges idea is something I had in mind for a while. Things such as events and random mini-bosses are already there in a very simple way (The witch mini-boss at the library or the Wendigo stalking you through the whole stage.) but I'm still thinking of a more efficient way to make the player interact with those events, so for now they're just visual for the most part.